The manufacture of artificial tubular casings from cellulosic materials has been practiced for many years, particularly for use in the processing of frankfurters and other sausage-shaped products; for example, salami and bologna. There are two general methods for preparing such artificial tubular cellulosic casings. In the first method the artificial casings are formed from a plastic-state cellulosic material which is extruded into tubular form. The extruded tubular casings, which are seamless, are then washed, dried and otherwise processed according to methods known to those skilled in the art prior to using such casings in the production of sausages. In the second method the artificial tubular casings are formed and seamed from a rollstock cellulosic film of definable width and thickness by passing the rollstock film over forming collars and mandrels of various geometries familiar to those skilled in the art. The longitudinal edges of the rollstock film, which edges can be oriented longitudinally or helically, are overlapped for a distance and joined to form a seam. The casings manufactured by this second method can be made on-line, just prior to stuffing with the desired sausage product, or off-line. When manufactured off-line, the finished, seamed tubular casing is typically wound in layflat form before shirring, usually with accordion-like folds, into a hollow stick, or onto a rod or tube, for end use on the sausage manufacturing equipment. When the tubular casings are manufactured, especially when made off-line and shirred, it has been found that certain prior art proposals such as seams which are mechanically formed, formed dry or water-wetted, with or without thermal treatment, do not have sufficient strength to withstand the forces encountered during the shirring and/or sausage manufacturing steps.
The term "cellulosic material(s)" as used herein means a material which is based on cellulose and is to be understood to include all suitable forms of such cellulose based material including cellophane, regenerated cellulose, cellulose hydrate and cellulose derivatives such as, for example, cellulose ethers and cellulose esters. In addition, the term cellulosic material(s) includes proteins, collagens, alginates, starches and other naturally occurring polymeric materials which are suitable for and may be used in the manufacturing of tubular casings sausages and sausage-like products.
The term "rollstock film(s)" as used herein means a cellulosic rollstock film that is either uncoated or coated. A coated rollstock film is thus a composite material in which one or more functional coatings have been applied to either or both sides of a cellulosic film. Herein, the word "coated" and "composite" may be used interchangeably. The functional coating may be either continuous or discontinuous on either side of the rollstock film and is typically a composition which acts to modify the mechanical, biological or chemical characteristics of the cellulosic material. For example, the coating may increase the tear strength or decrease permeability of the cellulosic film or it may render the cellulosic material waterproof. A discontinuous coating may cover only that part of the film which will not be overlapped. In connection with the present invention, highly successful results are obtained with uncoated cellulosic materials. Coatings or composites as discussed can be used provided the bonding process and permeability are not seriously hindered.
A wide variety of substances have been used to bond the overlapping edges of the tubular casings formed, either on-line or off-line, from the cellulosic or composite cellulosic rollstock films described above. U.S. Pat. No. 2,607,696 to Kunz describes sealing or joining together a hydrophilic sheet material (e.g., a cellulosic material such as regenerated cellulose rollstock film) by the use of acidified solutions of water-soluble, partially polymerized, heat-hardening resins such as an urea-formaldehyde resin or a melamine-formaldehyde resin. U.S. Pat. No. 3,595,667 to Turbak et al. describes sealing or joining sheets or films of regenerated cellulose or fiber-reinforced regenerated cellulose using a mixture of a polymeric polyisocyanate and an activator such as a polyol. U.S. Pat. Nos. 4,399,839 and 4,528,225 to Hutschenreuter et al. describe sealing or joining the longitudinal edges of a cellulose material by the use of a substantially water-soluble cationic resin which is a condensation product selected from the group consisting of a polyamide-polyamine including an aliphatic polyamine or polyamide with bifunctional halohydrins or derivatives thereof. U.S. Pat. No. 4,713,135 to Bridgeford describes the use of an aqueous zinc chloride, together with heat and pressure, to seal or join the overlapping edges of a cellulosic material.
Additional disclosure of methods for sealing or joining the overlapping edges of cellulosic materials or synthetic polymer materials, alone or in combination with cellulosic materials, may be found in the following U.S. Patents:
U.S. Pat. No. 2,575,467, to Reichel et al., which describes helical windings of strip material in forming stuffing casings with an overlap to form a joint which may be sealed with a sealing liquid that can include a basic solvent for the strip material;
U.S. Pat. No. 2,685,770, to Conti, which describes seamed casing formed by folding about a stuffing horn a flexible sheet of alkali-sensitive material such as regenerated cellulose to define overlapped edges which are sealed by an adhesive which may be an alkaline solution;
U.S. Pat. No. 2,773,773, to Harder et al., which describes the application of a solvent to thermoplastic, thermosetting or cellulosic materials, or to filaments applied to such materials, to promote sealing or joining of overlapping edges of such materials; examples in the case of cellulosic materials being a regenerated cellulose solvent adhesive such as tribenzylmethylammonium hydroxide, an alkali soluble cellulose ether or sodium hydroxide;
U.S. Pat. No. 3,640,734, to Oppenheimer et al., which describes the use of polyvinyl alcohol/polyvinyl ester copolymer films for forming tubular casings and the use of adhesives such as plasticized polyvinyl alcohol or polyvinyl alcohol/polyvinyl ester copolymers, solutions of polyvinyl alcohol copolymers in volatile organic solvents, or reactive adhesives such as isocyanates and epoxies;
U.S. Pat. No. 4,230,041, to Bailey et al., which describes the use of synthetic rubber, epoxy resins, acrylic compounds, and unsaturated compounds having vinyl groups as adhesives for bonding thermoplastic materials to a fibrous material made from synthetic plastics materials (for example, polyolefins, polyamides, polyacrylates or polyesters), or plant materials such as jute or cotton, or cellulose derivatives such as rayon;
U.S. Pat. Nos. 4,397,337 and 4,401,136, to Porrmann et al., which describe the use of thermoplastic or thermosetting synthetic resins as adhesives for seaming regenerated cellulose materials; examples of such adhesives being ethylene/vinyl acetate copolymers, low molecular weight polyethylene, atactic polypropylene, styrene/isoprene copolymers, copolymers containing carboxyl groups, fusible polyesters, polyurethanes, polyamides and polyaminoamides;
U.S. Pat. No. 4,399,839, to Hutschenreuter et al., which describes the use of an adhesive selected from the group consisting of polyamide-polyamine, an aliphatic polyamine or a polyamide with bifunctional halohydrins;
U.S. Pat. Nos. 4,410,011 and 4,401,135, to Andra et al., which describe adhesive materials including water soluble proteins (gelatin, egg albumin and glutenin) and cationic, thermosetting resins such as those described by Porrmann et al. in the patents cited above;
U.S. Pat. No. 4,517,254, to Grapentin et al., which describes activating a polyimide film to break .dbd.N--C(O)-- imide bonds, reacting the broken bonds with a polyamine to provide terminal amine groups and binding metal ions such as copper or nickel ions to such amine groups;
U.S. Pat. Nos. 4,709,447, 4,727,625, 4,944,069, 4,965,910, 4,972,547, 4,972,548 and 5,019,012, to Townsend et al., which describe helically formed, elongated casing having overlapping side edges sealed by frictional cohesiveness, which cohesiveness typically is enhanced by application of moisture (i.e., water) to the casing material;
U.S. Pat. Nos. 4,736,775 and 4,879,123, to Oxley, which describe the use of pressure sensitive adhesive tape(s) to seal the opposing lateral, overlapping edges of a casing material formed into tubular shape;
U.S. Pat. No. 4,806,395, to Walsh, which describes treating polyimide films with alkali and an amine to open the polyimide ring system and provide a means whereby metal ions can be coordinated to the polyimide for the purpose of initiating electroless plating; and
U.S. Pat. Nos. 4,879,123, to Siebrecht, and 4,940,614, to Kastl et al., which describe the use of an adhesive tape to seal opposing, overlapping edges of a film material formed into a tubular shape.
Each of the various United States patents referred to herein is incorporated by reference hereinto.
While the art of longitudinally or helically seaming or joining cellulosic materials has thus been the subject of many patents and other publications, no seaming approach has been described which is satisfactory in all aspects for the manufacturing of tubular cellulosic casings from rollstock cellulosic film. Inevitably, each of the prior art methods of seaming or joining has resulted in one or more problems. For example, in some cases the cellulosic material at the seam is either weakened by application of the functional adhesive coating or the cellulosic material is distorted during the seaming process. In other cases, the bond between the cellulose and the adhesive is too weak for consistent and reliable performance. The seaming process sometimes requires duplication of processing steps which adds to the expense of manufacturing the final sausage or sausage-like product. Lastly, and perhaps most importantly from a consumer viewpoint, adhesive materials used in the joining or seaming process typically must be applied at a width and/or thickness which results in a final product that has a longitudinal or spiral band of different color or shade of intensity than the bulk of the final product. While the band may not affect cooking or taste, it detracts from visual appeal, a very important aspect of all food products. Since the prior art approaches of seaming or joining cellulosic films typically results in such defects, a real need exists for an inexpensive approach for seaming or joining cellulosic materials that provides final products which will ultimately not have this objectionable visual band.
It is an object of the present invention to provide an improved method or process for producing, either on-line or off-line, a seamed, tubular casing by forming rollstock cellulosic film into a tube and longitudinally fusing, that is, bonding, seaming or joining, the edges of the film using the novel fusing agents disclosed herein. The novel fusing agents used in the invention are generically termed "organometallic solvents".
It is another object of the invention to provide casings using the novel fusing agents which allow the agent-fused, -seamed, -bonded or -joined region of the cellulosic film to maintain its integrity throughout the entire forming, moisture conditioning, shirring (when formed off-line) and food processing steps used in the manufacturing of a finished sausage or sausage-like product.
It is an additional object of the present invention to provide a fusing agent which produces a seamed or joined region of sufficient strength to withstand the mechanical or other stresses placed upon the seam during the manufacture of a final sausage or sausage-like product.
It is a further object of the invention to provide a fusing agent which will rapidly provide a seamed or joined region of the tubular casing produced from rollstock film so that when the casing is made either on-line for immediate sausage-making use or off-line for future use after shirring and other processing, the fused, seamed or joined casing may be put to such uses within the minimum possible time.
Another object of the invention is to provide casing having sufficient seam bond strength rapidly after fusing agent application such that additional moisture can be applied to the film immediately following the forming and bonding operation to provide optimum film moisture content for further processing.
Other objects and advantages to using the invention will become evident to those skilled in the art upon reading the details of the description of the invention.